<!DOCTYPE html>
<html lang="en">
<head>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8" />
    <title></title>
</head>
<body>
<div id="canvas-warp">
    <canvas id="canvas"></canvas>
</div>

<script>
    var canvas = document.getElementById("canvas");
    canvas.width = 500;
    canvas.height = 500;
    canvas.style.border = "1px solid #555";

    var ctx = canvas.getContext("2d");

    for(var i = 0 ; i < 6 ; i ++){
        for( var j = 0 ; j < 6 ; j++){
            ctx.strokeStyle = 'rgb(0,' + Math.floor(255-42.5*i) + ',' +
            Math.floor(255-42.5*j) + ')';

            ctx.beginPath();
            ctx.arc(12.5+j*25,12.5+i*25,10,0,Math.PI*2,true);
            ctx.stroke();
        }
    }
</script>
</body>
</html>